Advancing technology continues to pressure manufacturers to produce complementary metal-oxide semiconductor (CMOS) devices with both greater capacities and smaller profiles. To counteract the resulting parasitic effects caused by resistance/capacitance delays in gate electrodes in such down-scaled devices, there is a continual quest for new combinations of materials from which to fabricate gate structures. For example, in W/WNx/Poly-Si Gate Technology for Future High Speed Deep Submicron CMOS LSIs, 497–500 IEDM 1994, K. Kasai et al. describe a structure comprising tungsten, tungsten nitride and polysilicon (W/WNx/PolySi). This structure has a greatly reduced sheet resistance and enables improved performance of the CMOS device. The structure proposed by Kasai et al. is, however, limited because the structure is only able to withstand temperatures up to 900° C. for 30 seconds or less during rapid thermal annealing. Proper source/drain reoxidation requires temperatures at or above 900° C. for at least fifteen minutes. To date, where the W/WNx/PolySi structure is used, after source/drain reoxidation the wordline profile exhibits a considerable protuberance on the exposed tungsten silicide (WSix). This complicates subsequent etches, and the undesirable “spacer” implants from the gate edge decrease device performance.
In conventional processing, a conductive gate electrode is patterned into fine features by photo/etch processing. This electrode is subsequently subjected to reoxidation to repair physical damage caused by the etch process in one of two ways: either directly or through a deposited silicon dioxide spacer. For a tungsten silicide feature, this reoxidation results in SiO2 growth on the polysilicon and silicide. Other choices for metal shunt layers of polysilicon include materials such as tungsten, titanium silicide and molybdenum. As described by Robert Beyers in Thermodynamic considerations in refractory metal silicon-oxygen systems, 147–52 Journal of Applied Physics 56(1), (July, 1984), these metals, when oxidized, result in unstable metal oxides. This is because, unlike tungsten silicide, there is little or no silicon available for oxidation into SiO2.
As a result, there remains a need to be able to tap the potential of devices manufactured from materials such as tungsten and minimize the detrimental effects resulting from the formation of oxide.